There's not much "must see" in San Antonio.
You may not even want to stop at the Alamo to be honest. It's worth it just to drive by.
If you're into history like that check out one of the missions directly south of the city
Art, I've always loved McNay, it's the first place I saw Georgia Okeefes and they have a solid pop art gallery.
If there's anything you must do in San Antonio it's food and the easiest place for that is Mi Tierra Cafe y Panaderia, you can't go wrong with anything on the menu
Chachos used to have great margaritas but I don't think that's the case anymore
I'm partial to Shipleys donuts. Legit my favorite donut place in all of the country
And that's really it
It's a big ass suburb, with history to the south and mainly lives off festivals and the spurs.